New Zealand Warriors coach Andrew Webster has admitted he disagreed with the decision to send Dylan Walker to the sin bin at the back-end of the first half during the club's loss to the Melbourne Storm on Tuesday evening.

The Warriors, who were up 18-12 at the time, found themselves reduced to 12 men on either side of halftime shortly after losing Tohu Harris for the remainder of the game to a knee injury.

The tackle, which occurred on halfway, originally saw an error called after Eliesa Katoa was roughed into the ground and appeared to drop the ball.

He was taken from an immediate head injury assessment, with bunker official Ben Cummins taking the time to review the incident, before referee Grant Atkins sent Walker packing.

"It's a head slam," Atkins said at the time on-field.

"How's it a head slam?" Walker retorted.

"It has been reviewed, it's a head slam, you come in over the top. In you go," Atkins concluded.

Warriors' coach Andrew Webster said he disagreed with the decision, and on first look, had moved on to discussing the next play in attack with his coaching staff, such was his lack of worry over the decision.

"My reaction was that Dyl [Dylan Walker] was taking him to the ground and unfortunately, he [Eliesa Katoa] was head slammed and Dyl came over the top," Webster said.

"Because they wanted to check it, I looked and went 'oh he is sweet'. I wanted to have a good look and watch the replay and thought, awesome.

"Then I started turning to the next part we were talking about as a staff. I turned back around and they were calling him out, giving him ten.

"I just thought initially it was a really good tackle driving him to the ground. I didn't see any arm around his head or slamming his head to the ground. I didn't see that.

"When you're in the box, you're probably not seeing those things clearly because you're a bit biased, but I thought Dyl was fine."

Walker's time in the sin bin only cost his side a single try - to Nick Meaney after halftime - with the Storm then skipping away during the second half to record a win.

The Warriors utility, who has played five-eighth in recent weeks, will now await any charge handed down by the NRL's match review committee on Wednesday morning.